Process of tanning with borated methylol phenols



PROCESS OF TANNING WITH BORATED METHYLOL PHENOLS Daniel E. Nagy, Stamfrd, Conn. assignor to American Cyanamid Company, New York, N. Y., a corporation of Maine N0 Drawing. Application November 14, 1949, Serial No. 127,265

6 Claims. (Cl. 894.24)

This invention relates to water-soluble resinous compositions and more particularly, to new leather tanning agents and to processes for tanning skins and hides by means of these new agents.

Ordinary phenol-formaldehyde resins are soluble in water only at pH values above about 9 to 10. However, it is not possible to use such high pH values in tanning a skin because the skin becomes badly swollen and accordingly such phenolic resins have been applied only in solvent tannage, and then only experimentally.

In the past it has been customary to sulfonate ordinary phenol-formaldehyde resins and thus render them soluble in neutral and acid media. However, this sulfonation decreases in part the tanning action of the phenol resins and, since they have been rendered completely water soluble, they are to a greater or lesser extent capable of being extracted from leather particularly under severe conditions of use, such as obtains in the use of sole leather, army shoes, etc.

It is an object of the present invention to produce new water-soluble resinous compositions.

Another object of the present invention is to provide new tanning agents for hides and/or skins.

It is another object of the present invention to provide processes for tanning skins and/or hides.

A further object of the present invention is the production of light-colored full leather.

It is an object of the present invention to provide a process for tanning depickled or bated skins.

Still another object of the present invention is the production of resinous tanning agents which are soluble at pH values above about 6.5.

it is a further object of the present invention to provide new tanning agents for hides and/or skins which may be used in conjunction with other tanning agents such as ligno-sulfonate, vegetable tannins, mineral tanning agents, synthetic tanning agents, and the like.

Another object of the present invention is the preparation of a dried phenolic tanning agent which is completely stable against polymerization under normal storage condltions.

It is still another object of the present invention to provide leather tanning agents which, in finished leather products, are water-insoluble.

A further object of the present invention is the production of tanned leather from which the tanning agent cannot be extracted by water during use .as are ordinary tannins and the like.

Another object of the present invention is the provision of modified phenolic tanning agents which are soluble in water at pH values of from 7 to 8.

It is an object of the present invention to prepare phenolic tanning agents which can be applied to skins and/ or hides from water solution.

A further object of the present invention is the treatment of skins and/or hides first with a water-soluble phenolic resin tanning agent and then with salt and/or acid to fix the resin in the skin and/or hide in which state it becomes impervious to extraction by water under all conditions of use, even the most severe.

It is another object of the present invention to treat skins and/or hides first with a water-soluble borated phenolic resin tanning agent of the present invention and then with a different tanning agent which may be vegetable, mineral, or synthetic. I

It is yet another object of the present invention to treat leather tanned with a vegetable, mineral or synthetic tanning agent with a water-soluble borated phenolic resin of the present invention.

2,701,749 Patented Feb. 8, 1955 ice The above and other objects are attained by condensing a phenol with formaldehyde and borax under alkaline conditions and finally treating skins and/or hides or pretanned leather with the borated phenol-formaldehyde product obtained.

The invention will be described in greater detail in conjunction with the following specific examples in which proportions are given in parts by weight. The examples are merely illustrative, and it is not intended that the scope of the invention be limited to the details therein set forth.

Example 1 91.2 parts (0.4 mol) of di(hydroxylphenyl)dimethylmethane 97.2 parts (1.2 mol) of formaldehyde, 37%

43.6 parts (0.10 mol) of sodium hydroxide, 10%

parts of water Borax All of the above components except the borax are mixed together and heated at 75 C. for 2.3 hours. The borax is then added slowly, and a clear viscous solution which is dilutable with water is obtained. The concentrated syrup has a pH of 8.0 and a 10% solution of the syrup in water, a pH of 7.9. The resin is dried at a low temperature to produce 174.2 parts of a colorless glassy water-soluble solid.

Example 2 391.5 parts (4.16 mol) of phenol 185 parts (2.29 mol) of formaldehyde, 37% 20 parts of hydrochloric acid, 10%

62.5 parts of sodium hydroxide, 36%

506 parts (6.25 mols) of formaldehyde, 37% 15 8 parts of borax The 185 parts of formaldehyde are added gradually during 35 minutes with stirring to the phenol acidified with the hydrochloric acid at C. Heating is continued for 5 hours. The mixture is then cooled to 50 C. and made alkaline by addition of the sodium hydroxide. The 506 parts of formaldehyde are then added, and the clear red solution obtained is heated for 4% hours at 64-65 C.

The course of the condensation is determined by the following qualitative test: A sample of about 0.7 cc. is Withdrawn and mixed with a small amount of borax. This mixture is warmed, diluted with water, treated with solid carbon dioxide and warmed to a temperature of from 25-30 C. At the start of the condensation the borax dissolves without apparent reaction. After about the second hour of reaction the addition of borax to the sample effected a-marked increase in viscosity. Similarly, at the beginning of the reaction the addition of carbon dioxide causes precipitation of a bulky solid while as the reaction proceeds, the precipitate forms more slowly and in smaller amount. The reaction is considered complete when the solution becomes only slightly cloudy on addition of solid carbon dioxide, and no precipitate is formed on warming, stirring, or standing for 5 minutes.

When the reaction is complete the clear red solution, while still warm, is diluted with about 175 parts of water and the borax is then added. It dissolves readily to form a viscous, orange-colored solution which is further diluted with about parts of water, poured on trays and allowed to air-dry. The dried product is a light orange, brittle, glassy solid which dissolves slowly to give a clear, light red solution in water. The resin, which is soluble in water, is precipitated by dilute salt solutions. The yield of dried product is 718.4 parts.

Example 3 parts (1.0 mol) of resorcinol 162 parts (2.0 mols) of formaldehyde, 37%

77.6 parts (0.175 mol) of sodium hydroxide, 10% 50.4 parts borax The sodium hydroxide solution and resorcinol are mixed together and the formaldehyde is added at 20 C. in 15 minutes. The mixture is maintained at 20 23 C. for 20 minutes and the borax is then added whereupon the temperature rises to 28 C. After 30 minutes at 28-32 C. the viscous, clear, lights-colored solution is poured onto trays and allowed to air dry. A water-soluble, dark colored, glassy solid is produced.

Example 4 110 parts (1.0-mol) of resorcinol 162 parts (2.0 mols) of formaldehyde, 37%

77.6 parts (0.175 mol) of sodium hydroxide, 10%

100 parts borax I The procedure of Example 3 is followed. A water- 'soluble product, somewhat lighter in color than that of Example 3, is obtained.

Example 5 110 parts 1.0 mol) of resorcinol 162 parts (2.0 mols) of formaldehyde, 37% 77.6 parts (0.175 mol) of sodium hydroxide, 100 parts of borax Example 6 Q 476 parts of pickled lime split cowhide is depickled to a pH of 7.2-7.5 and washed with water until relatively salt free.

84 parts of the phenol-borax resin of Example 2 are dissolved in 500 parts of water by warming, and the cooled solution is then added to the washed stock and tumbled for two days.

At the end of the first day salt is added in portions so that the solution eventually contains 2% salt. At the end of the second day acetic acid is added to lower the pH to about 5.0.

The well tanned leather, with a shrinkage temperature of 84 C., is washed in water and fatliquored with a mixture of 6% of a sulfonated oil and 2% of neats-foot o1 The dried leather is full, lightbrown, and exceedingly strong and flexible;

Similar results are obtained when an equivalent amount of bated stock is substituted for the pickled lime split cowhide.

Example 7 Pickled lime split cowhide is tanned exactly as in Example 6. After the skin has been acidified to pH 5.0 there is added 100% by weight of a calcium base sulfite liquor (50 B.) obtained as a waste product in the sulfite process for the manufacture of paper. The skin is drummed overnight in the liquor, and hydrochloric acid is added gradually to lower the pH to about 4.0.

After 24 hours, when the lignin sulfonate has penetrated completely, the skin is washed and fatliquored as in Example 6.

The finished leather is more plump and firm than that of Example 6, and there is proportionally a much higher weight yield per pound of original hide.

Example 8 Pickled calfskins are tanned with chrome in the usual fashion and after the chrome has been set with alkali the skins are washed. well and treated with 5% of the resin of Example 1 dissolved in 50% by weight of warm water. The resin solution is preferably added in two or three equal feeds to the chome calfskin floated in 75% by weight of water. After drumming for two hours the leather is washed and fatliquored in the usual fashion.

Example-9 Pickled goatskins are depickled to a pH of 7 and washed. The skins ara drained and weighed. For each 100 lbs. of skins there is-used 20% by weight, of the resin of Example 2 dissolved in 100 lbs. of water. This is drummed for l.5 hours and during the next hour 3 lbs. of salt and 1 lb. of acetic acid are added in portions. The tannin material is now taken up completely as shown by the absenceof a precipitate in the liquor. The skins are then further acidified to a pH of about 4' with acetic and sulfuric acids,"and finally washedand fatliquored with/4% of a' sulfonated oil in 100% water. The finished skin,whi'ch is well tanned and possesses a; smoothv grain,.is .plurnp. and. alight. yellow tan .color.

4 Example 10 Pickled calfskins are weighed, depickled to a pH of 7 and washed. For each 100 lbs, of skin there are added 11 lbs. of the resin of Example 2 in 200 lbs. of water, and the skins are drummed for about 18 hours. 100 lbs. of 10% salt are added and after drumming an additional 3 hours 100 lbs. of 10% alum are added. There is no precipitate formed and after drumming for 2 hours the pH is 4.2. The skins are finally washed and fatliquored.

The leather which is light, almost white, in color is quite firm.

Example 11 Skins tanned with the borated phenol resin as in Example 7 are further tanned with 100 lbs. of soda base sulfite lignin (50 B.) obtained as a waste product in the sulfite process for the manufacture of paper, and lactic acid is added to lower the pH to 3.5. After drumming for about 18 hours the skins are washed and fatliquored.

, The resulting leather is very light tan shade.

plump and of a pleasing Example 12 15 parts of the product of Example 4 are dissolved in 300 parts of water and 100 parts of calfskin depickled to a pH of 7.4 are tumbled in this solution for about 16 hours. The pH of the solution is lowered to about 4.0 by addition of acetic acid and tumbling is continued for anotlber 3 hours. The shrinkage temperature is then 94 The leather is fatliquored with 4% of a sulfonated oil and finished in the usual manner. It is a firm, full,

' brown leather.

' Phenol or m-cresol may be condensed directly with formaldehyde under alkaline conditions in the preparation of my new resinous compositions; or condensation products, preferably under acid conditions, of two or more mols of phenol or m-cresol or a mixture of phenol and m-cresol with one mol of an aldehyde or a ketone such as, for example, formaldehyde, acetone, acetaldehyde, furfural, etc., may be further condensed, under alkaline conditions, with formaldehyde. The products of such pre-condensations depending, of course, on the conditions of the condensations may be pure compounds of the type of di(phydroxyphenyl) methane, di(p-hydroxyphenyl) dimethylmethane, 1,1-di(p-hydroxyphe'nyl) ethane, di(p-hydroxyphenyl) furyl methane, di(2-methyl-4-hydroxyphenyl) methane, 1 (p-hydroxyphenyl)-1-(2-rnethyl-4-hydroxyphenyl) ethane, etc., or they may be mixtures of these dihydroxy compounds with the corresponding triand tetra-hydroxy compounds. Dihydric phenols as resorcinol and catechol may also be reacted with formaldehyde under alkaline conditions or first to form the corresponding bis compounds and finally under alkaline conditions. The expression a phenol" hen used in the present specification and claims is intended to include all of the above-specified types of compounds.

Tanning propertiesof my new resinous compositions vary somewhat. Good tanning agentsunder normal conditions are obtained from phenol and rn-cresol only if they are pre-condensed under acid conditions to form a his orlike compound or mixture of compounds. Variations in tanning procedure, however, make possible the use of condensation products of phenol or m-cresol with formaldehyde and borax under alkaline conditions as sole tanning agents and, moreover, such alkaline-condensed resins markedly enhance the tannage obtained when used with other tanning agents such as sulfide lignin under normal conditions of tanning.

Formaldehyde-yielding materials such as paraformaldehyde may be substituted for the formaldehyde of the examples.

Relative molar proportions of phenol, based on the number of hydroxyaryl groups, to formaldehye in the alkaline condensation will range from about 1:1 to about 1:2, the preferred molar ratio being about 121.5.

In general I prefer to first form an alkaline condensation product of phenol and formaldehydeand then react the condensation product with borax. As is well known to anyone skilled in the art, the amount of alkali'and the temperature of condensation will vary depending upon the reactivity of the phenol, and the exact conditions of the reaction form no part of the present invention. I generally use from about.0.'l';to 0.2 .mol of sodium or potassium hydroxide per mol of phenol, based on the number of hydroxyaryl groups, i. e., compounds of the type of di(p-hydroxyphenyl) methane contain two hydroxyaryl groups Whereas the dihydric phenol resorcinol, for example. contains only one, but I am not limited to these quantities. Particularly can I use more than 0.2 mol of the alkali per mol of phenol since a large excess does no harm and indeed, if a very low reaction temperature is used, larger amounts of alkali may be required. Equivalent quantities of other alkalis such as, for example, sodium carbonate, potassium carbonate, sodium bicarbonate and the like may be substituted for the sodium or potassium hydroxide; the pH of the solution should be about 10. It is desirable to keep the quantity of alkali to a minimum so that the final pH of the condensation product will be about 7. If it is higher, the product must be neutralized before addition of borax.

The optimum reaction temperature for the formation of my new resinous compositions will vary from about 5570 C. for the alkaline condensation of monohydric phenol, i. e., phenol or m-cresol or corresponding poly compounds, with formaldehyde to from about 15-30 C. for the similar condensation of resorcinol. In the former case the borax is added to and reacted with the condensation product at the same temperature, i. e., 55 -70 C., while in the latter case, the reaction mixture is heated to about 2550 C. when the borax is added.

It is frequently possible, as in Example 5, to condense the phenol, formaldehyde and borax under alkaline conditions in a single step. The optimum reaction temperature is then from about 50100 C.

The preceding reaction temperatures are the optimum temperatures, not the only operative temperatures, and my invention is not limited to these ranges. In general I can prepare my new resinous compositions at from 0-100 C.

Relatively large amounts of borax are used for reaction with phenol-formaldehyde condensation products in the preparation of the tanning agents of the present invention. I use from about 25%75% or more by weight of borax based on the weight of phenol. The borax is not added as a catalyst or merely in catalytic quantities; it actually reacts with the phenol-formaldehyde condensation product and forms a part of my final product. The borax in the preparation of the new resinous compositions of my invention may be replaced entirely or in part by boric acid or other salts of boric acid which are at least as soluble in water as borax such as sodium metaborate, potassium tetra-borate and the like.

The present invention contemplates for use as tanning agents those borax-resin complexes which are soluble in water at a pH above about 6.5. I have found that in a neutral solution, solubility of the phenol-formaldehydeborax condensation products increases with the number of methylol groups present and, of course, decreases with increase in the degree of polymerization. My preferred resins are those which contain two or three phenol nuclei joined by methylene or corresponding groups. If the molecular weight of the resin is much higher than this, it will not be soluble in water.

The new resinous tanning agents of the present invention may be used alone or in conjunction with other tanning agents such as ligno-sulfonate, vegetable tannins, mineral tanning agents, synthetic tanning agents including formaldehyde, and the like. In the latter case, my new tanning agents may be used to after-tan leather already pre-tanned with another tanning agent or agents, or skins and/or hides may be first tanned with the new agents and then with a tanning agent of another type. Particularly advantageous results are obtained when the borated methylol phenols of the present invention are used for tanning in conjunction with ligno-sulfonate.

If my borated phenolic resins are used alone in the process of the present invention, I prefer to use from 15% to 20% or more by weight of resin, based on the pickled weight or white weight of hides or skins; if they are used in combination with other tanning agents, I prefer to apply from 5% to 10% by weight of resin; based on the pickled weight or white weight of the hides or skins. Generally, from 1% to 50% of resin, on the same basis as above, may be applied in my process.

When initial tannage of skins and/or hides with my new resins is contemplated, substantially salt-free depickled or bated stock must be provided since the resins are precipitated by salt. They are also precipitated by acid but nevertheless may be used for after-tannage of, for example chrome leather, because only a surface tannage is involved.

It is an advantage of the present invention that the use of borax in the production of my borated phenol-formaldehyde condensation products markedly improves the color of the resins. Thus, the borated methylol phenol resins, when used as tanning agents, produce light colored leathers.

It is another advantage of the present invention that methylol phenol resins which are soluble only in strongly alkaline solution form borax complexes which are soluble at a pH as low as 7 and which are therefore valuable tanning agents.

A further advantage of the present invention lies in the fact that my borated resins may be dried to water-soluble solids. Moreover, in the dry form, they are completely stable against polymerization upon storage for indefinite periods of time under normal storage conditions.

I claim:

1. A process which comprises treating substantially salt-free skins or hides with an aqueous solution at a pH 'of at least about 6.5 of a water-soluble polymerizable condensation product obtained by condensing under alkaline conditions a formaldehyde-reactive phenol with formaldehyde in relative molar proportions of from about 1:1 to about 1:2 and at least about 25 per cent of borax, based on the weight of phenol, and subsequently insolubilizing the condensation product in the skins or hides.

2. A process according to claim 1 in which said condensation product is fixed in the skins or hides by addition of an acid.

3. A process according to claim 1 in which said phenol is phenol and said condensation product is fixed in the skins or hides by addition of an acid.

4. A process according to claim 1 in which said condensation product is obtained by condensing phenol with formaldehyde in relative molar proportions of about 2:1 under acid conditions, continuing the condensation with additional formaldehyde under alkaline conditions, the relative molar proportions of phenol to formaldehyde in said alkaline condensation being from about 1:1 to about 1:2, and then treating the resulting methylolated product with at least about 25 per cent of borax, based on the weight of phenol.

5. In a combination tannage process, the treatment of substantially salt-free skins or hides according to the process of claim 1.

6. A process which comprises treating substantially salt-free skins or hides with an aqueous solution at a pH of at least about 6.5 of a water-soluble polymerizable product of the condensation under alkaline conditions of a substance, said substance being selected from the group consisting of phenol, meta-cresol, dihydric phenols, partial condensates thereof with an aldehyde, and partial condensate thereof with a ketone, with formaldehyde in relative molar proportions of from about 1:1 to about 1:2 and at least about 25 per cent of borax, based on the weight of said substance, and subsequently insolubilizing the condensation product in the skins or hides.

References Cited in the file of this patent UNITED STATES PATENTS 1,191,480 Schmidt July 18, 1916 1,216,612 Schmidt Feb. 20, 1917 2,012,928 Hassler Aug. 27, 1935 2,204,512 Russell et al June 11, 1940 2,385,373 Rhodes Sept. 25, 1945 2,398,331 Rust Apr. 9, 1946 2,469,428 Beachell May 10, 1949 2,512,708 Beachell June 27, 1950 2,519,842 Maaskant Aug. 22, 1950 OTHER REFERENCES Jour. Soc. Lea. Trades Chem., vol. XXXIII, August 1949, No. 8, pp. 291-299; May 1949, pp.169176, articles by Hough.

Progress in Leather, Science, 1920-1945, pp. 261 and 262, pub. 1948 by B. L. M. R. A., London, England.

Lichtenstein article in B. L. M. R. A. Lab. Reports 1945, vol. 24, pp. 142-145. 

1. A PROCESS WHICH COMPRISES TREATING SUBSTANTIALLY SALT-FREE SKINS OR HIDES WITH AN AQUEOUS SOLUTION AT A PH OF AT LEAST ABOUT 6.5 OF A WATER-SOLUBLE POLYMERIZABLE CONDENSATION PRODUCT OBTAINED BY CONDENSING UNDER ALKALINE CONDITIONS A FORMALDEHYDE-REACTIVE PHENOL WITH FORMALDEHYDE IN RELATIVE MOLAR PROPORTIONS OF FROM ABOUT 1:1 TO ABOUT 1:2 AND AT LEAST ABOUT 25 PER CENT OF BORAX, BASED ON THE WEIGHT OF PHENOL, AND SUBSEQUENTLY INSOLUBILIZING THE CONDENSATION PRODUCT IN THE SKINS OR HIDES. 